Opaque low resistivity silicon carbide

ABSTRACT

An opaque, low resistivity silicon carbide and a method of making the opaque, low resistivity silicon carbide. The opaque, low resistivity silicon carbide is a free-standing bulk material that may be machined to form furniture used for holding semi-conductor wafers during processing of the wafers. The opaque, low resistivity silicon carbide is opaque at wavelengths of light where semi-conductor wafers are processed. Such opaqueness provides for improved semi-conductor wafer manufacturing. Edge rings fashioned from the opaque, low resistivity silicon carbide can be employed in RTP chambers.

BACKGROUND OF THE INVENTION

[0001] The present invention is directed to an opaque, low resistivitysilicon carbide. More specifically, the present invention is directed toan opaque, low resistivity silicon carbide that is opaque within aspecific wavelength of light.

[0002] Silicon carbide, especially silicon carbide produced by chemicalvapor deposition (CVD-SiC), has unique properties that make it amaterial choice in many high temperature applications. Chemical vapordeposition processes for producing free-standing silicon carbidearticles involve a reaction of vaporized or gaseous chemical precursorsin the vicinity of a substrate to result in silicon carbide depositingon the substrate. The deposition reaction is continued until the depositreaches the desired thickness. To be free standing, the silicon carbideis deposited to a thickness of upward of about 0.1 mm. The deposit isthen separated from the substrate as a free-standing article that may ormay not be further processed by shaping, machining, or polishing and thelike to provide a final silicon carbide article.

[0003] In a chemical vapor deposition silicon carbide production run, asilicon carbide precursor gas, such as a mixture ofmethyltrichlorosilane (MTS), hydrogen and argon, is fed to a depositionchamber where the mixture is heated to a temperature at which themixture reacts to produce silicon carbide. Hydrogen scavenges chlorinethat is released from the MTS when the MTS dissociates during thereaction. An inert, non-reactive gas such as argon or helium is employedas a carrier gas for MTS (a liquid at room temperature). Inert gasesalso act as a diluent whose flow rate can be varied to optimize thereaction and assures removal of by products from the reaction/depositionzone. The silicon carbide deposits as a layer or shell on a solidmandrel provided in the deposition chamber. After the desired thicknessof silicon carbide is deposited on the mandrel, the coated mandrel isremoved from the deposition chamber and the deposit separated therefrom.The monolithic free-standing article may then be machined to a desiredshape. Several CVD-SiC deposition systems are described in U.S. Pat.Nos. 5,071,596; 5,354,580; and 5,374,412.

[0004] Pure CVD-SiC has relatively high electrical resistivity. Whilethis is a desirable characteristic for certain applications, such acharacteristic is a limitation restricting its use in otherapplications. Certain components, such as plasma screens, focus ringsand edge rings used in plasma etching chambers need to be electricallyconductive as well as possess high temperature stability. While hightemperature properties of CVD-SiC have made it a material of choice foruse in such chambers, its high resistivity has limited its use infabricating components that require a greater degree of electricalconductivity.

[0005] High electrical resistivity of CVD-SiC has further restricted itsuse in applications that are subject to the buildup of staticelectricity. The need to ground components used in such applicationsrequires that they possess greater electrical conductivity than isgenerally found in CVD-SiC. A low resistivity silicon carbide wouldprovide a unique and useful combination of high temperature propertieswith suitable electrical conductivity properties for use in applicationswhere grounding is required.

[0006] U.S. patent application Ser. No. 09/790,442, filed Feb. 21, 2001,(non-provisional of provisionally filed U.S. application No. 60/184,766,filed Feb. 24, 2000), assigned to the assignee of the presentapplication discloses a chemical vapor deposited low resistivity siliconcarbide (CVD-LRSiC) and method of making the same. Electricalresistivity of the silicon carbide is 0.9 ohm-cm or less. In contrast,the electrical resistivity of relatively pure silicon carbide, prior tothe CVD-LRSiC of the application Ser. No. 09/790,442, is in excess of1000 ohm-cm. The method of preparing the CVD-LRSiC employs many of thesame components as the CVD methods disclosed above except that nitrogenis also employed. The lower resistivity of the silicon carbide isbelieved to be attributable to a controlled amount of nitrogenthroughout the silicon carbide as it is deposited by CVD. The nitrogenis incorporated in the deposit by providing a controlled amount ofnitrogen with the precursor gas in the gaseous mixture that is fed tothe reaction zone adjacent a substrate. The reaction is carried out inan argon gas atmosphere. As the silicon carbide precursor reacts to formthe silicon carbide deposit, nitrogen from the gaseous mixture isincorporated into the deposit. The CVD-LRSiC contains at least 6.3×10¹⁸atoms of nitrogen per cubic centimeter of CVD-LRSiC.

[0007] While the resistivity of CVD-SiC can theoretically be lowered toa desired level by the introduction of a sufficient amount ofimpurities, the resulting elevated levels of impurities adversely affectother properties of the SiC such as thermal conductivity and/or hightemperature stability. The CVD-LRSiC is relatively free of impurities,containing less than 10 ppmw of impurity trace elements as determined bygas discharge mass spectroscopy. The CVD-LRSiC is further characterizedby thermal conductivity of at least 195 Watts/meter degree Kelvin (W/mK)and a flexural strength of at least 390 MPa.

[0008] The CVD-LRSiC is electrically conductive and possesses hightemperature stability in addition to being a high purity SiC. Thus, thefree standing CVD-LRSiC may be readily employed in high temperaturefurnaces such as semiconductor processing furnaces and plasma etchingapparatus. The CVD-LRSiC may be sold as a bulk material or may befurther processed by shaping, machining, polishing and the like toprovide a more finished free-standing article. For example, theCVD-LRSiC may be machined into plasma screens, focus rings andsusceptors or edge rings for semi-conductor wafer processing and othertypes of high temperature processing chamber furniture as well as otherarticles where CVD-LRSiC material is highly desirable.

[0009] In the manufacture of semi-conductor wafers, there are numerousprocess steps. One set of steps is referred to as epitaxial deposition,and generally consists of depositing a thin layer (between about 10 toless than one micron) of epitaxial silicon upon the wafer. This isachieved using specialized equipment such as SiC wafer boats or SiCsusceptors or edge rings to secure the semi-conductor wafers inprocessing chambers, and a chemical vapor deposition (CVD) process. TheCVD process requires that the wafer be heated to very high temperatures,on the order of 1200° C. (2000° F.).

[0010] There has been a recent trend in the semi-conductor art to employequipment that operates upon a single wafer, rather than a group ofwafers. In single wafer equipment the heating of the wafer to the CVDtemperature is greatly accelerated such that the wafer is taken fromabout room temperature to an elevated temperature within about 30seconds. Such processing is known as rapid thermal processing or RTP.RTP includes depositing various thin films of different materials by anRTP-CVD process, rapid annealing of wafers (RTP thermal processing) andrapid oxidation to form silicon dioxide. While the silicon wafer canaccept such rapid temperature change well, the wafer must be held inposition by a susceptor or edge ring that can also withstand such rapidtemperature changes. Susceptor or edge rings composed of CVD-SiC orCVD-LRSiC have proved very suitable for withstanding RTP conditions.

[0011] Many RTP systems employ high intensity W-halogen lamps to heatsemi-conductor wafers. Pyrometers are used to measure and to controlwafer temperature by controlling the output of the W-halogen lamps.Accurate and repeatable temperature measurements for wafers over a widerange of values are imperative to provide quality wafers that meet therequirements for integrated circuit manufacturing. Accurate temperaturemeasurement requires accurate radiometric measurements of waferradiation. Background radiation from W-halogen lamps (filamenttemperature of about 2500° C.) or from other sources can contribute toan erroneous temperature measurement by the pyrometer especially at lowtemperatures (about 400° C.) where the radiant emission from the waferis very low compared to the lamp output. Also, any light from theW-halogen lamps that passes through (transmits) a susceptor or edge ringcan cause an incorrect temperature reading by the pyrometer.

[0012] The industry has addressed the temperature problems by designingthe RTP chamber with single sided heating and mounting the pyrometers onthe chamber bottom opposite the light source. To further reduce lightinterference, the area under the wafer was made “light tight”, thuseliminating stray reflected light from entering the area under thewafer. In addition to redesigning the RTP chamber, CVD-SiC or CVD-LRSiCedge rings and susceptors were made opaque to W-halogen lamp light inthe wavelength range that pyrometers operate by coating the rings with200 μm (0.008 inches) of poly-silicon. However, coating edge rings withpoly-silicon adds substantial cost to the edge rings. Further, thecoating process (epitaxial silicon growth) has many technical problemsassociated with it such as dendritic growth, bread loafing around edgesand purity problems that reduce yields. Poly-silicon coating addsthermal mass to the edge rings. The increased thermal mass limitsheating ramp rates during RTP processing cycles. Ideally, edge ringshave a thermal mass that is as low as possible to achieve the fastestheating ramp rates. The faster the ramp rate the shorter the processingcycle time for wafers, thus reducing wafer processing costs. Anotheradvantage to faster ramp rates is that the total integrated time at hightemperature for the wafers is reduced allowing for less diffusion of anydopant species employed during processing. Such is highly desirable asthe feature sizes decrease for semi-conductor devices (trend in thesemi-conductor industry). As the feature size gets smaller the distancetraveled by dopant atoms also gets smaller.

[0013] Accordingly, although there are highly suitable CVD-LRSiCarticles that may be employed in semi-conductor wafer processingchambers, there is still a need for improved CVD-LRSiC articles that areopaque at certain wavelengths.

SUMMARY OF THE INVENTION

[0014] The present invention is directed to free standing, opaque lowresistivity silicon carbide that has a resistivity of less than 0.10ohm-cm, and a process for making the opaque low resistivity siliconcarbide. The opaque low resistivity silicon carbide is opaque to lightin a wavelength range of from about 0.1 μm to about 1.0 μm at atemperature of at least about 250° C. Because the low resistivitysilicon carbide (LRSiC) is opaque at wavelengths of light from about 0.1μm to about 1.0 μm, the low resistivity silicon carbide advantageouslymay be employed as furniture in semi-conductor processing chambers whereaccurate maintenance of semi-conductor wafer temperatures are desired.Since the low resistivity silicon carbide is opaque at wavelengths oflight from about 0.1 μm to about 1.0 μm, light from heating lampsemployed in wafer processing chambers does not pass through the lowresistivity silicon carbide, thus allowing a more accurate reading ofwafer temperatures. Accordingly, defects in wafers caused by impropertemperatures are reduced or eliminated.

[0015] Further, because the low resistivity silicon carbide need not becoated with poly-silicon to provide the appropriate opaqueness, suchproblems as dendritic growth, bread loafing and the high cost of coatingare eliminated. Also, the problem of adding thermal mass to siliconcarbide articles is eliminated. Thus, faster heating ramp rates forrapid thermal processing are achieved with articles prepared from thelow resistivity silicon carbide of the present invention. The fasterheating ramp rates in turn provide for reduced total integrated time athigh temperatures for wafers and reduced diffusion of dopant duringprocessing.

[0016] The opaque, low resistivity silicon carbide of the presentinvention is prepared by chemical vapor deposition. High concentrationsof nitrogen are employed in the CVD process. Reactants are mixedtogether with the high concentrations of nitrogen in a CVD chamber, andthe silicon carbide product is deposited on a substrate such as amandrel. The CVD deposited silicon carbide when exposed to a temperatureof at least 250° C. is opaque at light wavelengths of from about 0.1 μmto about 1.0 μm. In addition to having low resistivity and to beingopaque to light at wavelengths of from about 0.1 μm to about 1.0 μm, thesilicon carbide is stable at high temperatures, has a high thermalconductivity and is of a high purity. The opaque, low resistivitysilicon carbide may be removed from the mandrel and retained in bulkform or may be shaped, machined and polished to provide a final article.

[0017] A primary objective of the present invention is to provide for afree standing, low resistivity silicon carbide.

[0018] Another objective of the present invention is to provide for afree standing, low resistivity silicon carbide that is opaque to lightat wavelengths of from about 0.1 μm to about 1.0 μm.

[0019] A further objective of the present invention is to provide athermally stable free standing, low resistivity silicon carbide.

[0020] An additional objective of the present invention is to provide afree standing, low resistivity silicon carbide that has a high purity.

[0021] Other objectives and advantages of the present invention may beascertained by a person of skill in the art after reading the followingdisclosure and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic of a CVD apparatus that may be used tofabricate opaque, low resistivity silicon carbide;

[0023]FIG. 2A is a top view of an edge ring composed of CVD depositedopaque, low resistivity silicon carbide; and

[0024]FIG. 2B is a cross-section of an edge ring composed of CVDdeposited opaque, low resistivity silicon carbide.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Chemical vapor deposited (CVD) silicon carbide of the presentinvention has low electrical resisitivity of less than 0.10 ohm-cm, andis opaque to light at wavelengths of from about 0.1 μm to about 1.0 μmat a temperature of at least about 250° C. Such silicon carbide is bulkor free-standing, i.e., capable of being self-supported. Bulk orfree-standing silicon carbide is distinguished from thin film siliconcarbide which are deposited upon a surface with the intent that thesilicon carbide remain permanently bonded to the surface. Bulk orfree-standing silicon carbide can be machined and polished to a desiredsize and shape. Such silicon carbide may be employed as furniture inprocessing chambers for chemical vapor deposition (CVD), rapid thermalprocessing (RTP), epitaxial deposition and the like. In addition tohaving a low resisitivity and being opaque to light at wavelengths offrom about 0.1 μm to about 1.0 μm, the opaque, low resistivity siliconcarbide has a high thermal conductivity, high flexural strength, andhigh thermal stability. The opaque, low resistivity silicon carbide isrelatively free of metallic impurities containing less than about 5 ppmwof impurity trace elements such as boron, phosphorous and the like asdetermine by gas discharge mass spectroscopy. Additionally, the opaque,low resistivity silicon carbide has reduced thermal mass. All numericalranges are inclusive and combinable in the present application.

[0026] The opaque, low resistivity silicon carbide is prepared bychemical vapor deposition. To provide an opaque, low resistivity siliconcarbide, high concentrations of nitrogen are incorporated into the CVDsilicon carbide. High concentrations of nitrogen are incorporated intothe silicon carbide by providing a high concentration nitrogenatmosphere for the silicon carbide precursors to react. Nitrogenatmosphere means that no inert, non-reactive gases such as argon, heliumor other noble gas is employed in preparing the opaque, low resistivitysilicon carbide. The atmosphere composes greater than 32% by volume ofnitrogen, preferably at least about 40% by volume of nitrogen.Preferably the atmosphere composes from about 45% to about 50% by volumeof nitrogen. The remainder of the atmosphere is composed of hydrogen gasand silicon carbide precursors as well as water vapor. Nitrogen isincorporated into silicon carbide in amounts of greater than 1.5×10¹⁹ toas high as about 2×10¹⁹ to about 3×10¹⁹ atoms of nitrogen per cubiccentimeter of silicon carbide. While not being bound to theory, nitrogenis believed to act as a dopant that reduces band gaps in the siliconcarbide to reduce resistivity. Nitrogen may be employed in any suitableform such as N_(2(g)), volatile organic compounds containing —NO₂ oramine groups such as —NH₂, compounds of —N(H)₄ ⁺ and quaternary amines,NO₃ ⁻ salts in aqueous form, halogen containing nitrogen compounds, andthe like. Examples of suitable nitrogen compounds include NF₃ and NH₃.

[0027] Silicon carbide precursor is selected from materials that can bereacted to form silicon carbide. Such materials include a component,such as a silane or a chlorosilane, which can react to form a siliconmoiety and a component such as a hydrocarbon that can react to form acarbon moiety. The component contributing the silicon moiety can bedifferent from, or can be the same as, the component contributing thecarbon moiety. Hydrocarbon substituted silanes are preferred siliconcarbide precursors because they contain both the silicon carbidemoieties in a single compound. The precursor(s) can be a compound whichdissociates at the reaction conditions forming one or both of thesilicon carbide moieties, or the precursors can be two or more compoundswhich react to provide one or both of the moieties. While theprecursor(s) needs to be in the gas phase when reacted in the vicinityof the substrate, it is not necessary that the precursor's boiling pointbe less than ambient temperature. Methyltrichlorosilane (MTS) is apreferred precursor, especially when used with hydrogen (H₂), whichscavenges chlorine released when MTS dissociates. Since MTS providesboth silicon and carbon in a stoichiometric ratio of about 1:1, no othersource of silicon and carbon moieties is required. H₂/MTS molar ratioranges from about 2 to about 10, preferably from about 4 to about 7.Hydrogen partial pressure ranges from about 75 torr to about 100 torr,preferably from about 85 torr to about 95 torr. MTS partial pressureranges from about 10 torr to about 25 torr, preferably from about 15torr to about 20 torr.

[0028] Nitrogen may be provided in any suitable form as long as the formis sufficiently volatile or may be made sufficiently volatile to form agas. Nitrogen partial pressures range from about 80 torr to about 110torr, preferably from about 90 torr to about 105 torr. No inert,non-reactive gases such as argon, helium or other noble gas is employedin preparing the opaque, low resisitivity silicon carbide.

[0029] Deposition chamber pressures range from about 100 torr to about300 torr, preferably from about 150 torr to about 250 torr. Depositionchamber temperatures range from about 1250°C. to about 1400° C.,preferably from about 1300° C. to about 1375° C.

[0030] Deposition substrates may be composed of any suitable materialthat can withstand the harsh conditions of the deposition chambers. Anexample of a suitable substrate or mandrel for depositing siliconcarbide is graphite. Graphite mandrels as well as other types ofmandrels may be coated with a release agent such that deposited siliconcarbide may be readily removed from the mandrel after deposition.Silicon carbide deposits may be removed from mandrels by controlledoxidation (controlled combustion).

[0031] An example of a chemical vapor deposition system for producingopaque, low resistivity silicon carbide articles of the presentinvention is illustrated in FIG. 1. Deposition is carried out withinfurnace 10. A stainless steel wall provides a cylindrical depositionchamber 12. Heating is provided by a graphite heating element 14 whichis connected to an external power supply by an electrode 16. Graphitedeposition mandrels are arranged within a graphite isolation tube 20 andgas is introduced by means of an injector 22 through the upper end ofthe isolation tube so that the reaction gases sweep along mandrels 18.One or more baffle(s) 24 is used to control the aerodynamics of gas flowthrough furnace 10.

[0032] Line 26, which supplies injector 22, is fed by a nitrogencylinder 28, a hydrogen cylinder 30, and a MTS bubbler 32. Nitrogen isfed by lines 34 and 36 both directly to inlet line 26 and throughbubbler 32. The hydrogen cylinder 30 is connected by line 38 to theinlet line 26. Nitrogen flow through lines 32 and 36 and hydrogen flowthrough line 38 are controlled by mass flow controllers 40, 42, and 44.The MTS bubbler 32 is maintained at a constant temperature by a constanttemperature bath 46. A pressure gauge 48 is connected to a feed backloop that controls the gas pressure of bubbler 32.

[0033] Outlet line 50 is connected to a bottom outlet port 51. Pressurewithin the deposition chamber 12 is controlled by a vacuum pump 52 whichpulls gases through the chamber and a furnace pressure control valve 54operably connected to the vacuum pump. Temperature and pressure withindeposition chamber 12 are measured by thermal probe 58 and pressureindicator 56. Exhaust gases are passed through filter 60 to removeparticulate material upstream of the pressure control valve and througha scrubber 62 downstream of the vacuum pump to remove HCl.

[0034] After deposition the bulk or free-standing low resistivitysilicon carbide may be sold in bulk form or further processed byshaping, machining, polishing and the like to form a desired article.Further processing involves numerous methods that are well known in theart for free-standing silicon carbide. Such methods often involvediamond polishing and machining. An example of an article made from thelow resistivity silicon carbide is a susceptor or edge ring employed tohold or secure semi-conductor wafers for processing in furnaces or othersuitable chambers.

[0035] Advantageously, when the free-standing low resistivity siliconcarbide is exposed to a temperature of at least about 250° C. thesilicon carbide becomes opaque at light wavelengths of from about 0.1 μmto about 1.0 μm, preferably from about 0.7 μm to about 0.95 μm. Lowresistivity silicon carbide may remain opaque to light at wavelengths offrom about 0.1 μm to about 1.0 μm to temperatures of up to about 1450°C. At such wavelengths, silicon carbide articles do not transmit lightand are highly suitable for furniture in semi-conductor processingchambers. Such chambers include, but are not limited to, RTP processingchambers where pyrometers that operate at wavelengths of about 0.7 μm toabout 0.95 μm monitor semi-conductor wafer temperatures. Such RTPchambers may operate at temperatures of from about 300° C. to about1250° C. Opaque low resistivity silicon carbide of the present inventionremains opaque to light at wavelengths of from about 0.1 μm to about 1.0μm at such temperatures. Since the opaque, low resistivity siliconcarbide does not transmit light at wavelengths where pyrometers operate,temperature readings of semi-conductor wafers are more accurate whenprocessed on furniture composed of the silicon carbide of the presentinvention. Thus, fewer defects occur in processed wafers and costefficiency is improved.

[0036] Since the opaque low resistivity silicon carbide is opaque tolight wavelengths at which a pyrometer operates, susceptors or edgerings employed in RTP need not be coated with poly-silicon. Accordingly,articles composed of silicon carbide within the scope of the presentinvention eliminate the problems of epitaxial silicon growth such asdendritic growth, bread loafing and any impurities that may occur duringthe poly-silicon coating process. Such impurities may lead tocontamination of semi-conductor wafers during RTP. Elimination of thepoly-silicon coating process also reduces over-all coat of makingsilicon carbide articles as well as processing semi-conductor wafers.

[0037] Additionally, elimination of unnecessary coatings on edge ringsreduces the thermal mass of the edge ring and further improves the RTPin semi-conductor wafer manufacturing. Reduced thermal mass permitsfaster ramp rates in RTP, thus reducing semi-conductor processing cycletime, and reducing wafer processing costs. Further, as ramp ratesincrease the total integrated time at high temperature for wafers isreduced allowing for less diffusion of any dopant species in the RTP.Reduced diffusion of dopant species into semi-conductor wafers in turnpermits features on the wafers to be decreased (an industry goal).

[0038] Low electrical resistivity of the silicon carbide of the presentinvention is also desirable for radio frequency (RF) heated susceptorsto couple the RF field to the susceptor and for components in the plasmaetch chamber to couple the plasma energy to the component. In addition,due to low resistivity the wafer holders can be grounded and do notbuild a static charge on them. Articles made from the low resistivitysilicon carbide include, but are not limited to, edge rings or susceptorrings, wafer boats, epi susceptors, and plasma etch components such asgas diffusion plates, focused rings, plasma screens and plasma chamberwalls, and the like. Because the silicon carbide of the presentinvention has a low resistivity, the silicon carbide may be employed ascomponents in electrical devices such as electrodes and heatingelements. Chemically vapor deposited low electrical resistivity siliconcarbide prepared by the method of the present invention may have anelectrical resistivity of less than 0.50 ohm-cm. Preferred siliconcarbide prepared by the method of the present invention has anelectrical resistivity of less than 0.10 ohm-cm, and most preferredsilicon carbide has an electrical resistivity of from about 0.005 ohm-cmto about 0.05 ohm-cm.

[0039]FIGS. 2A and 2B show an edge ring machined and polished from asingle piece of opaque, low resistivity silicon carbide within the scopeof the present invention. Edge ring 100 has a circular circumferencecomposed of main ring component 102 with wafer holding flange 104continuous with main ring component 102. Wafer holding flange 104terminates at edge 106 to form void 108. FIG. 2B is a cross-section ofedge ring 100 along line A-A. Main ring component 102 terminates at anouter surface in support flange 110 that is continuous with main ringcomponent 102. Main ring component 102 terminates at an inner surfacewith flange 112 which is continuous with wafer holding flange 104, thussecuring wafer holding flange 104 to main ring component 102.

[0040] Although FIGS. 2A and 2B show an edge ring as a circular article,any suitable shape may be employed. A circular edge ring is illustratedin FIGS. 2A and 2B because many semi-conductor wafers are in a circularshape. Size and thickness of the edge ring may also vary considerable.However, the thinner the edge ring, the more suitable the ring is forprocessing semi-conductor wafers. A thinner edge ring can heat up fasterin wafer processing furnaces than a relatively thick edge ring, thusreducing the amount of processing time. Thickness of opaque lowresistivity silicon carbide edge rings may range from about 0.1 mm toabout 1.0 mm, preferably from about 0.25 mm to about 0.5 mm.

[0041] The following examples are intended to further illustrate thepresent invention and are not intended to limit the scope of theinvention.

EXAMPLE 1

[0042] Free-standing opaque, low resistivity silicon carbide wasprepared in an apparatus similar to the apparatus illustrated in FIG. 1.Deposition temperature in the CVD chamber was about 1350° C. andpressure was about 200 torr. Hydrogen partial pressure was about 90torr, nitrogen partial pressure was about 93 torr (a nitrogen content ofabout 46.5% by volume of the CVD chamber), and MTS partial pressure wasabout 17 torr. No inert or noble gases were employed in the CVD process.Silicon carbide was deposited onto a graphite mandrel coated with arelease agent. The deposition process was performed over about 48 hours.The process produced an edge ring that was opaque to light at awavelength range of from about 0.7 μm to about 0.95 μm at temperaturesof about 300° C. and higher.

[0043] A control free-standing silicon carbide bulk material was alsoprepared. The control free-standing silicon carbide was prepared by thesame process as described above except that nitrogen was not employed.Instead, argon gas was used. The argon gas partial pressure was about 93torr. Deposition was performed over about 48 hours.

[0044] After deposition, silicon carbide from each mandrel was removedand machined to form an edge ring similar in shape and dimensions asshown in FIGS. 2A and 2B. The bulk resistivity of the edge ring preparedusing nitrogen instead of argon gas was measured on four witness samplestaken at four locations around the ring. The bulk resistivity rangedfrom about 0.009 ohm-cm to about 0.015 ohm-cm.

[0045] The bulk resistivity of the silicon carbide produced in thechamber containing argon gas ranged from about 1.0 ohm-cm to about 100ohm-cm from samples taken from four locations. The edge ring preparedwith argon gas in the chamber was coated with about a 200 μm ofpoly-silicon by an epitaxial silicon growth process to make the ringopaque to light at wavelengths of from about 0.7 to about 0.95 μm at RTPtemperatures.

[0046] The low resistivity edge ring was fabricated to a thickness toachieve the same thermal mass as the poly-silicon coated silicon carbidering. The control ring had a nominal thickness of about 0.25 mm withabout a 200 micron silicon coating. The low resistivity silicon carbidering had a nominal thickness of about 0.36 mm. This was done to obtain ahead-to-head comparison of the ring performance.

[0047] Each edge ring was then employed in RTP to test their thermalperformance in processing semi-conductor wafers. A semi-conductorsilicon wafer was placed in each edge ring. The edge rings with theirsemi-conductor wafers were placed in an RTP Radiance® apparatus forprocessing. The temperature in the RTP apparatus was raised from about20° C. to about 1200° C. over about 10 seconds. The heat source in theRTP apparatus was a high intensity W-halogen lamp (filament temperatureabout 2500° C.). The temperature of each semi-conductor wafer wasmonitored by an optical pyrometer (operating at a light wavelength offrom about 0.7 μm to about 0.95 μm). Temperature uniformity of eachsemi-conductor wafer was measured about the same and less than 10degrees over the duration of processing.

[0048] Although both edge rings were opaque to light at the wavelengthof from about 0.7 μm to about 0.95 μm and performed about the same, theedge ring coated with poly-silicon was more costly to prepare because ofthe additional coating step and material. Thus, even though both ringsperformed well, the edge ring of the present invention was still animprovement over the coated edge ring because it was less costly tomanufacture.

EXAMPLE 2

[0049] A free standing opaque, silicon carbide edge ring having a shapesimilar to the edge ring illustrated in FIGS. 2A and 2B was prepared bythe same process as in Example 1 above with a high concentrationnitrogen atmosphere. As in Example 1 above, the bulk resistivity of theedge ring was measured at four locations and ranged from about 0.009 toabout 0.015 ohm-cm. The edge ring had about a 30% lower thermal massthan the edge ring in Example 1 because its thickness was about 0.25 mmversus about 0.36 mm for the edge ring in Example 1 and there was nopoly-silicon coating. The low resistivity silicon carbide edge ring wasopaque to light at a wavelength of from about 0.7 μm to about 0.95 μm ata temperature of about 300° C. and higher.

[0050] A silicon wafer was placed in the edge ring and the assembly wasplaced into an RTP Radiance® for similar thermal testing as inExample 1. The temperature of the RTP chamber went from about 20° C. toabout 1200° C. in about 10 seconds. The low resistivity silicon edgering was opaque to light at a wavelength of from about 0.7 μm to about0.95 μm during the wafer processing. The heat source in the RTP chamberwas a W-halogen lamp (filament temperature of about 2500° C.). Thetemperature of the wafer was monitored by an optical pyrometer(operating at a light wavelength of from about 0.7 μm to about 0.95 μm).

[0051] Temperature uniformity around the edges of the wafer fluctuatedon the average about 5 centigrade degrees. Thus, temperature uniformitywas better than the coated and uncoated edge rings of Example 1. Also,less lamp power (about 20% less), and therefore longer lamp life, wasneeded to achieve the process temperature cycles to process the wafer.The edge ring had been cycled (employed as a wafer holder) over 2,000times in an RTP chamber and still continued to perform well, i.e., wafertemperature uniformity, high ramp rates, reduced lamp power.

What is claimed is:
 1. A free-standing article comprising lowresistivity silicon carbide having an electrical resistivity of lessthan 0.10 ohm-cm.
 2. The free-standing article of claim 1, wherein theelectrical resistivity of the low resistivity silicon carbide is fromabout 0.005 ohm-cm to about 0.05 ohm-cm.
 3. The free-standing article ofclaim 1, wherein the low resistivity silicon carbide is opaque to lightat a wavelength of from about 0.1 μm to about 1.0 μm at a temperature ofat least about 250° C.
 4. The free-standing article of claim 3, whereinthe low resistivity silicon carbide is opaque to light at a wavelengthof from about 0.1 μm to about 1.0 μm at a temperature of from at leastabout 250° C. to about 1450° C.
 5. The free-standing article of claim 1,wherein the low resistivity silicon carbide is opaque to light at awavelength of from about 0.1 μm to about 1.0 μm at a temperature of fromabout 300° C. to about 1250° C.
 6. The free-standing article of claim 3,wherein the low resistivity silicon carbide is opaque to light in awavelength range of from about 0.7 μm to about 0.95 μm.
 7. Thefree-standing article of claim1, wherein the low resistivity siliconcarbide has a nitrogen content of greater than 1.5×10¹⁹ atoms/cm³. 8.The free-standing article of claim 7, wherein the low resistivitysilicon carbide has a nitrogen content of from about 2×10¹⁹ atoms/cm³ toabout 3×10¹⁹ atoms/cm³.
 9. The free-standing article of claim 1, whereinthe free-standing article is an edge ring or a susceptor ring, a waferboat, epi susceptors, electrodes, heating elements, plasma etchcomponents, and the like.
 10. The free-standing article of claim 9,wherein the plasma etch components comprise gas diffusion plates,focused rings, plasma screens, or plasma chamber walls.
 11. An edge ringcomprising low resistivity silicon carbide having an electricalresisitivity of less than 0.10 ohm-cm, the edge ring comprises acircular main ring component that terminates at an outer surface with asupport flange and terminates at an inner surface with a flange that iscontinuous with a wafer holding flange, the wafer holding flangeterminates to define a center void.
 12. The edge ring of claim 11,wherein the low resistivity silicon carbide has an electricalresistivity of from about 0.005 ohm-cm to about 0.05 ohm-cm.
 13. Theedge ring of claim 11, wherein the low resistivity silicon carbide isopaque to light at a wavelength of from about 0.1 μm to about 1.0 μm ata temperature of at least about 250° C.
 14. The edge ring of claim 13,wherein low resistivity silicon carbide is opaque to light at awavelength of from about 0.1 μm to about 1.0 μm at a temperature of fromat least about 250° C. to about 1450° C.
 15. The edge ring of claim 14,wherein the low resistivity silicon carbide is opaque to light at awavelength of from about 0.1 μm to about 1.0 μm at a temperature of fromabout 300° C. to about 1250° C.
 16. The edge ring of claim 13, whereinthe low resistivity silicon carbide is opaque to light from about 0.7 μmto about 0.95 μm.
 17. The edge ring of claim 1, wherein the edge ringhas a thickness of from about 0.1 mm to about 1.0 mm.
 18. The edge ringof claim 17, wherein the edge ring has a thickness of from about 0.25 mmto about 0.5 mm.
 19. The edge ring of claim 11, further comprising asemi-conductor wafer resting on the wafer holding flange.
 20. A methodof making a low resistivity silicon carbide article comprising reactingsilicon carbide precursors in a nitrogen atmosphere to form lowresistivity silicon carbide, and depositing the low resistivity siliconcarbide on a substrate.
 21. The method of claim 20, wherein the nitrogenatmosphere is greater than 32% by volume of nitrogen.
 22. The method ofclaim 21, wherein the nitrogen atmosphere comprises about 45% by volumeto about 50% by volume of nitrogen.
 23. The method of claim 26, whereinthe low resistivity silicon carbide comprises greater than 1.5×10¹⁹atoms of nitrogen/cm³.
 24. The method of claim 23, wherein the lowresistivity silicon carbide contains from about 2×10¹⁹ atoms ofnitrogen/cm³ to about 3×10¹⁹ atoms of nitrogen/cm³.
 25. The method ofclaim 20, wherein the low resistivity silicon carbide has an electricalresistivity of less than 0.1 ohm-cm.
 26. The method of claim 25, whereinthe low resistivity silicon carbide has an electrical resistivity offrom about 0.005 ohm-cm to about 0.05 ohm-cm.
 27. The method of claim20, wherein the low resistivity silicon carbide is prepared by chemicalvapor deposition.
 28. The method of claim 27, wherein a partial pressureof nitrogen in a chemical vapor deposition chamber is from about 80 torrto about 110 torr.
 29. The method of claim 28, wherein the partialpressure of nitrogen in the chemical vapor deposition chamber is fromabout 90 torr to about 105 torr.
 30. The method of claim 20, wherein thenitrogen is provided as nitrogen gas, volatile organic compoundscontaining —NO₂, amine groups, quaternary amines, compounds of —N(H)₄ ⁺,aqueous —NO₃ ⁻ salts, halogenated nitrogen compounds, NH₃ or mixturesthereof.
 31. The method of claim 30, wherein the nitrogen is provided asNF₃.
 32. The method of claim 20, further comprising exposing the lowresistivity silicon carbide to a temperature of at least about 250° C.to provide a low resistivity silicon carbide opaque at a lightwavelength of from about 0.1 μm to about 1.0 μm.
 33. The method of claim32, wherein the low resistivity silicon carbide is exposed to atemperature of from at least about 250° C. to about 1450° C. to providea low resistivity silicon carbide opaque to light at a wavelength offrom about 0.1 μm to about 1.0 μm.
 34. The method of claim 33, whereinthe low resistivity silicon carbide is exposed to a temperature of fromabout 300° C. to about 1250° C. to provide a low resistivity siliconcarbide opaque to light at a wavelength of from about 0.1 μm to about1.0 μm.
 35. The method of claim 32, wherein the low resistivity siliconcarbide is opaque to light at a wavelength of from about 0.7 μm to about0.95 μm.
 36. A method of making an opaque low resistivity siliconcarbide article by chemical vapor deposition comprising providingsilicon carbide precursor methyltrichlorosilane and hydrogen gas in anatmosphere of nitrogen gas at a partial pressure of from about 90 torrto about 105 torr; providing a reaction chamber temperature of fromabout 1250° C. to about 1400° C.; reacting methyltrichlorosilane andnitrogen gas to form a low resitivity silicon carbide deposit on amandrel, the low resistivity silicon carbide has an electricalresistivity of from about 0.005 ohm-cm to about 0.05 ohm-cm; andexposing the low resistivity silicon carbide to a temperature of atleast about 250° C. to provide a low resistivity silicon carbide opaqueto light at a wavelength of from about 0.1 μm to about 1.0 μm.
 37. Themethod of claim 36, wherein the low resistivity silicon carbidecomprises from about 2×10¹⁹ atoms of nitrogen/cm³ to about 3×10¹⁹ atomsof nitrogen/cm³.
 38. The method of claim 36, wherein the low resistivitysilicon carbide article is exposed to a temperature of at least about250° in an RTP chamber.
 39. The method of claim 38, wherein the lowresistivity silicon carbide article is an edge ring or susceptor ring.40. The method of claim 39, wherein the edge ring or susceptor ringcontains a semi-conductor wafer.